The perl interpreter can be built to allow the use of a site customization script.
By default this is not enabled,
to be consistent with previous perl releases.
To use this,
add -Dusesitecustomize to the command line flags when running the Configure script.
See also "-f" in perlrun.

Config.pm is now about 3K rather than 32K,
with the infrequently used code and %Config values loaded on demand.
This is transparent to the programmer,
but means that most code will save parsing and loading 29K of script (for example,
code that uses File::Find).

The socket() function on Win32 has been fixed so that it is able to use transport providers which specify a protocol of 0 (meaning any protocol is allowed) once more.
(This was broken in 5.8.6,
and typically caused the use of ICMP sockets to fail.)

Another obscure bug involving substr and UTF-8 caused by bad internal offset caching has been identified and fixed.

A bug involving the loading of UTF-8 tables by the regexp engine has been fixed - code such as "\x{100}" =~ /[[:print:]]/ will no longer give corrupt results.

Case conversion operations such as uc on a long Unicode string could exhaust memory.
This has been fixed.

index/rindex were buggy for some combinations of Unicode and non-Unicode data.
This has been fixed.

read (and presumably sysread) would expose the UTF-8 internals when reading from a byte oriented file handle into a UTF-8 scalar.
This has been fixed.

Several pack/unpack bug fixes:

Checksums with b or B formats were broken.

unpack checksums could overflow with the C format.

U0 and C0 are now scoped to ()pack sub-templates.

Counted length prefixes now don't change C0/U0 mode.

packZ0 used to destroy the preceding character.

P/ppack formats used to only recognise literal undef

Using closures with ithreads could cause perl to crash.
This was due to failure to correctly lock internal OP structures,
and has been fixed.

The return value of close now correctly reflects any file errors that occur while flushing the handle's data,
instead of just giving failure if the actual underlying file close operation failed.

not() || 1 used to segfault.
not() now behaves like not(0),
which was the pre 5.6.0 behaviour.

h2ph has various enhancements to cope with constructs in header files that used to result in incorrect or invalid output.

There is a new taint error,
"%ENV is aliased to %s".
This error is thrown when taint checks are enabled and when *ENV has been aliased,
so that %ENV has no env-magic anymore and hence the environment cannot be verified as taint-free.

The internals of pack and unpack have been updated.
All legitimate templates should work as before,
but there may be some changes in the error reported for complex failure cases.
Any behaviour changes for non-error cases are bugs,
and should be reported.

There has been a fair amount of refactoring of the C source code,
partly to make it tidier and more maintainable.
The resulting object code and the perl binary may well be smaller than 5.8.6,
and hopefully faster in some cases,
but apart from this there should be no user-detectable changes.

$^UTF8LOCALE has been added to give perl space access to PL_utf8locale.

The size of the arenas used to allocate SV heads and most SV bodies can now be changed at compile time.
The old size was 1008 bytes,
the new default size is 4080 bytes.

On UNICOS,
lib/Math/BigInt/t/bigintc.t hangs burning CPU.
ext/B/t/bytecode.t and ext/Socket/t/socketpair.t both fail tests.
These are unlikely to be resolved,
as our valiant UNICOS porter's last Cray is being decommissioned.

If you find what you think is a bug,
you might check the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at http://bugs.perl.org.
There may also be information at http://www.perl.org,
the Perl Home Page.

If you believe you have an unreported bug,
please run the perlbug program included with your release.
Be sure to trim your bug down to a tiny but sufficient test case.
Your bug report,
along with the output of perl -V,
will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
You can browse and search the Perl 5 bugs at http://bugs.perl.org/